PARASITES OF SIMULIUM LARVAE 91 
ovoid, filament about thirty to forty times the length of the 
spore. : 
III. Glugea multispora sp. nov. Pansporoblast polysporulate. 
Pansporoblast membrane not subpersistent. Spores about 4y x 
2.5. 
The earliest stages were never seen. It is conjectured, how- 
ever, that the parasite, which undoubtedly enters the body cavity 
through the alimentary tract, is able to parasitise only young 
larvae. This is thought to be due to the postembryonic devel- 
opment of the cephalic fans and peritrophic membrane, both 
of which are highly specialized organs and in Simulium larvae 
show unique and interesting modifications. The parasite was 
found attacking only the cells of the fat-body. These are soon 
ruptured and the parasite subsequently leads a free life in the 
body cavity of its host, where it grows to comparatively enor- 
mous volume, consisting of a multinucleate mass of protoplasm 
which greatly distends the body of its host. As the latter matures, 
the myxosporidium, as the parasite is now termed, is converted 
into innumerable thick-shelled spores. ‘These escape from the 
larva, which has succumbed to the attack, and by entering the 
alimentary tract of fresh larvae spread the disease. 
Since these parasites are to be found in all species of Simulium 
larvae present in the streams where they occur, it is probable 
that they could be transferred to fresh streams and thus cause 
the infection of species of Simuliym larvae in which as yet no 
parasites have been found. The parasite rarely, if ever, passes 
over into the adult, so that the natural spread of the disease 
from stream to stream is slow. That these Microsporidians are 
not widely distributed throughout the United States is indicated 
by the fact that though Simulium larvae have been carefully 
studied in several localities no cases of their presence have been 
recorded. When infected larvae are at all abundant in streams, 
their greatly distended and whitened abdomens are very conspic- 
uous, and are readily seen at some distance from the water, 
under conditions in which normal healthy larvae are almost or 
quite invisible. 
A further parasite in the fall generation, probably a Gregarine, 
has been found, infecting in some streams as many as half of 
